so uh... what IS it?

General Composites Discussions Products Talk
#1

tooling surface… gelcoat…

polyester, epoxy… whatever chemistry… what is it about gelcoats and tooling surface materials that makes them different / harder?

i realize its some sort of additive, i am assuming powders of some sort, metallic or not, that give these materials the durability and rigidity that they need…

but does anyone here actually know what they put in to these products to make them work?

i wouldnt mind trying to make my own, with some guidance, which i guess is what im getting at here. anyone here make their own home-brew tooling coats that work well and polish out nicely?

thanks for any input!

-david

#2

I’m signing on for the education as well.

#3

Silica flour is what most coats make them durable and scratch proof.

Glass flakes are a good option for abrasion resistance.

In addition to these kind of materials, expect to use some stabilising agents, rheology modifiers, etc. It can be quite interesting to arrive at a good coating.

#4

sounds complex.

OK, so lets start with “silica flour”. what is that exactly? fumed silica? or cabosil as ive heard it called?

next, glass flakes… are these different than chopped glass fibers? like really really tiny ones, essentially?

-david

#5

Producing a good quality tooling gelcoat is difficult. First is the base resin selection criteria. Base resins for tooling gel coats are specially formulated for this purpose and are seldom sold separately by the suppliers. It is their proprietary technology that that are letting out. Then there is their filler technology as well. Then also their promotor technology, this is critical for a number of factors. Low gassing, positive cure tooling gelcoat. another critical factor in using a good quality tooling gelcoat. There is a lot that goes in to producing a good quality tooling gelcoat.
The big thing is, do you want to do all of that work to a plug and then produce a mould that isn’t quite up to par? Big risk in my view. If you are producing a non critical part or a part that you want to do a short run on, then purchase a good quality gelcoat and ask for it to be pigmented at half or a quarter of its normal pigment strength. You don’t need opacity or uv resistance for a tooling gelcoat, you need the properties of the base resin to work for you in that gelcoat. Yes you can add silica flour, micro glass or even milled glass fibre to the mix as well. All of these will either increase abrasion resistance and improve hardness in the lower than normal pigmented gelcoat. Be mindful though when you add these fillers, you also change the cure characteristics of the gelcoat. Film thickness becomes even more critical.

#6

Fumed silica is another type. (Cabosil, Aerosil, etc). It is also used to adapt the viscosity and rheology of a resin, to make it a gelcoat. however, it is not silica flour.

Silica flour in basics is very, very fine sand.

Glass flakes are no fibers either. They are, uhh, flakes. Just like corn flakes. One of my customers uses it in a coating which is used on the inside of dredging pumps (pumps up to 8 ft in diameter). Very harsh conditions for a coating.

On epoxy or polyester:

For polyester production, use a polyester mould. Epoxy does not cope with the styrene attack, in the longer term.

For epoxy production you can use polyester or epoxy.

#7

The issue with fumed silica is ensuring the person blending the fumed silica has the correct blending equipment. Fumed silica needs to be sheared in to the gelcoat not stirred. If you stir you can almost guarantee that you will have un-dispersed fumed silica in the gelcoat. Not a great idea having un- dispersed fillers on the surface of a mould. The other thing that makes tooling gelcoats so good and critical for use is their gloss retention and the ability to impart a high gloss to the gelcoat. Sometimes adding a high degree of fillers can affect these properties.

#8

OK, then its definitely not as easy as i had hoped it would be.

it seems that in order to make a well performing tooling coat i would need to get another education in chemistry, and then add a few years of trial and error to nailing down the perfect formula…

since neither of those things is going to happen, i suppose ill skip it and just invest in good materials.

to ask a more pointed question though:

in our prototyping phase, this is the way im doing it. eventually if it all works out we would have proper tooling machined by a machine shop… or maybe i buy a nicer machine :slight_smile:

i am directly CNC machining female molds. in a perfect world, these would be made from aluminum or steel. my machine isn’t capable of that at this point. a step down from that is to use corian or other acrylic solid surface countertop material, which ive done a few times now have had great results.

at the lower-quality end of this spectrum i have been roughing the molds out of MDF. i over-machine the molds to about .020" past the OML. then i apply several layers of gelcoat and re-machine the gelcoat to the proper OML with a fine stepover, then sand, polish, etc etc etc.

can you guys recommend a good quality tooling coat or gelcoat for doing this? it needs to be sandable/polishable but still durable enough for scratch resistance.

at this point these molds are designed for infusion with epoxy. we may try other resin systems eventually like vinylester and or methacrylate, which seems very interesting…

thanks for any help, and for the education!

-david

#9

In that case I would recommend a (repairable) vinylester gelcoat. You could apply that over a PU primer, which seals the MDF.

Test your materials before using them in production, however.

#10

Hawaiian,
Sandable and polishable generally don’t go together when it comes to tooling gelcoats. Tooling gelcoats are designed to cure very hard. This aids in the gelcoat imparting a high degree of gloss and gloss retention throughout the life of the mould. What I have learnt over the years with tooling is to ensure that all of your work needs to start at the plug phase. Get your plug work right and the rest with flow from that point on. Get it wrong at that stage and it creates more work down the line that you did not allow for. OK, using gelcoat for finishing off a plug has its own set of problems as well. Ensure that you gain a positive cure to the gelcoat that you finish the plug with. I have experienced and have seen plugs that look great finished with a gelcoat, good gloss levels and relatively free from imperfections. Then the mould is made and when released the tooling gel coat is dull. Why? You haven’t achieved full film cure of the gelcoat on the plug. Gelcoats are designed to achieve a degree of full cure at a given film thickness. Compromise this and you won’t achieve the gloss you would have hoped for on the plug and ultimately the mould. So often I here, OH well I’ll work the mould to achieve the gloss and finish I require. Wrong, get the plug right! Good tooling gelcoats aren’t cheap why attack them with sandpaper? If you want to to use gelcoats to finish plugs off with then ensure your gelcoats are well cured. Either, apply the gelcoat at its correct film thickness or accelerate the cure with either patch-aid or patch booster if you are wanting to apply the gelcoat less than what is recommended. Do not use excessive amounts of catalyst either to compensate for thin applications as this will increase the chances of you getting porosity in the gelcoat. Avoid the colour white as well, it is the most difficult colour to pick an imperfection in. If you only have white, then small amounts of a chosen pigment or an alternative gelcoat colour you may small amounts of mixed in with white would be better.
VE tooling geloats are my preference nowadays as the cover so many different manaufcaturing methods.
Good elongation to break, good heat resistance and good chemical resistance. Most of the major gelcoat manufactures make one. The next thing is, do not use a VE for a tie layer in moulds. Use a VE/DCPD blended tie layer resin specifically designed for this purpose. You will achieve a positive cured cosmetically pleasing layup. Again, so often I see moulds made using pure VE’s as tie layers. Mould looks good for a few pulls, and then orange peel appears out of nowhere! Even on finsihed components use see this phenomenon.These type of tie layer resins are exclusively used by some of the major boat builders around the world to achieve A class high volume producing moulds. They also use these type of resins for their finished components as well. Your choice of structural resin is then up to you and your budget. You can chose a zero/low shrink filled or un-filled tooling resin, there are advantages and dis-advantages for both. That’s probably for another thread this post is getting long. Or a good quality positive curing “low exotherming” polyester. Generally not achievable in standard polyesters, but very achievable in DCPD resin systems. Both in ortho and iso’s. My preference would be iso DCPD’s as they have a higher elongation to break. Using these type’s of resins also assists in cure greatly. The old adage of leave the mould on the plug to allow the mould to cure, doesnt’t apply nowadays with these types of resin systems. Full cure is generally achieved the very next day or within hours depending on the system you chose. So it is advantageous to get the mould off the plug and allow the tooling gelcoat to cure off the plug not on. If and only if you need to sand the tooling gelcost do it as soon as you get it off the plug. Do not leave it for a few days as your work will get harder in more ways the one. Don’t attack the mould with orbital sanders either, always with wet sanding and a flexible sanding block is always preferred. If you get your plug right then the mould should only need a grit of no less than 1200, finer is even better. Or any at all!
Most of the major resin and gelcoat manufacturers will able to assist you with the above materials. If you net send me a message and will give reccomndations.
I hope this all has helped?